Grinding of organic materials



Patented Aug. 21, A 1951 GRINDING OFORGANI C MATERIALS Joseph W. Ayers,Easton, Pa., assignor to Agrashell; Inc., acorporationlof Delaware NoDrawing. Application July 15, 1946, Serial No. 683,768

10 Claims. 1

This invention relates to processes for grinding organic materials andmore specifically to the production of combustible materials in finelydivided form by procedures in which all danger of explosion, burning,decomposition of deterioration of the product due to oxidation or otherthe hazards arising from the presence of the oxygen.

In an effort to overcome these fire hazards, many safety devices andcut-out systems have been installed on grinding machinery to preventfires or their spreading and to localize explosions. Grinding systemsand processes have been designed wherein the avoidance of oxygen in themill is attempted by the introduction of inert gases such as carbondioxide, nitrogen and steam. Since most ground organic materialshowever, have limited commercial value, the use of carbon dioxide,nitrogen, or other inert gas, even when the same is recirculated throughthe system has been found to be unsuitable or too expensive forindustrial acceptance. To a limited extentwood flour has been ground onmill stones at temperatures below the boiling point of waterwhere there"is no fire hazard and also limited amounts of of water and sometimessteam have been applied to the stones to cool the same. This process'isemployed where ample waterpoweris available but is not satisfactory forgeneral use.

At the present time, various organic materials are ground on corrugatedand spiked differential rolls, in various attrition mills and in ballmills, but in spite of magnetic and other separating devices forremoving tramp metal, of various safety devices and of various cut-outsystems, such are not 100% efiicient. In spite of all precautions taken,serious explosions have occurred on many occasions and because ofinability to completely eliminate the explosion hazard, somemanufacturers have been forced to discontinue operation of their plants.1

It is an object of the present invention to provide a method of grindingcombustible" materials in sucha way as to prevent fires. and explosionsor injury to the material being ground.

Broadly considered, the present invention involves the grinding of heatand oxygen sensitive organic material in a normally hot operatinggrinding mill under a superatmospheric pressure of steam generated byvaporizationof a small amount of water introduced in the grindin mill.The water may be introduced into the millalong with the organic materialto be ground or may be introduced through a separate inlet into contactwith the organic material or the hot grindin elements. The vaporizationof the water in the mill takes up or dissipates the excess heatgenerated by the grinding operation and the vaporizing water or steampositively excludes oxygen from contact with the material being groundor the ground material.

The grinding operation of the present invention is not limited to anyparticular type of mill, for the grinding may be accomplished inconventional dry grinding hammer mills, attrition mills, mill stones,disk mills, roller mills or in disintegrators now used for or capable ofgrinding any of the many types of combustible materials contemplated bythe present invention. The mill employed, however, must .be totallyenclosed in order that the superatmospheric pressure required may bedeveloped and maintained. Sealed feed and discharge devices, such asrotary valves and interrupted or plug seal screw conveyors, must also beemployed. For the release of any excess steam generated in the mill, themill or conveying system may be provided with an asperating pipe fittedwith an adjustable damper so adjusted at all times as to keep the millatmosphere under pressure.

The process of the invention applies primarily to the production of fineparticle size powders and industrial flours from various combustibleorganic materials and particularly to very fine particle sizes such asthose which will pass a 100 mesh screen, a 200 mesh screen, a 325 meshscreen or still smaller sizes. It is not generally applicable to thegrinding of such materials to particles of coarse sizes in'excess ofmesh, for ordinarily high temperatures or other deteriorative conditionsare not encountered when'coarse'mesh material is produced. The processis applicable only to grinding in hot operating, dry-grinding mills, i.e. mills in which the motivating energy and internal friction loss inthe mill are high and where a considerable amount of heat is generatedin the mill which unless dissipated in some way will cause the abovedescribed'orgamc material 3 being ground to burn, explode, decompose, orotherwise be damaged by oxygen or other conditions.

The process of the invention is applicable to the treatment of a greatvariety of natural vegetable materials such as to wood for producin woodflour, to nut shells for producing nut shell flour and also to pits,seeds, roots, tubers, stems, fibers, barks, grains andhulls for theproduction of fillers, extenders, adhesives, agricultural dustingpowders and the like. The process is also applicable to the grinding ofmany synthetic combustible materials such as resins, organic Di mentsand other organic materials in general which do not appreciably softenat temperatures below 300 C.

In the grinding of natural vegetable materials by the processes of thepresent invention, the conversion of pentosans to furfural and organicacids such as acetic, formic, and gallic acids is avoided. Also theoxidation of the resin and wax content of such materials to undesirableend products is inhibited.

The grinding operation of the present invention may be efiicientlycarried out in an attrition mill. A suitable mill is one equipped with36 inch disks powered with '75 horse power motors on the respectivedisks which run in opposite directions. The heat dissipation factor ofthe present invention can be appreciated from the knowledge that the 150horse power connected load on this mill converted to heat energyrepresents approximately 380,000 B. t. u. per hour. In the grinding of amaterial to a fine particle size it is reasonable to assume that atleast 60% of the energy input is converted to heat by friction and withrespect to the 36 inch attrition mill the heat developed would amount toabout 230,000 B. t. u. per hour. In the operation of the process of thepresent invention an amount of water is continuously introduced into themill which dissipates sufficient heat to maintain the temperature belowthat at which fires, explosions or product decomposition will result,which amount of Water, of course, must not be suflicient to take thetemperature of the mill below the required 212 F. for otherwise asuperatmosphere of steam would not be maintained.

As hereinbefore indicated, the water removes or dissipates the excessheat through the latent heat of evaporation and the Water iscontinuously introduced into the mill at a predetermined and controlledrate. In commercial installations for operation of the presentinvention, the rate of flow of Water into the mill may be controlledautomatically by means of a thermostat in the mill wall connected to aneedle valve in a water feed line leadin to the mill, the controlinstrument being set at a given temperature above the boiling point ofwater. Through this arrangement, mill temperatures may be held within F.of the setting of the instrument. During the grinding operation underthe temperature conditions stated, steam is constantly generated in themill, thereby creating a positive pressure above atmospheric Within theenclosed mill (1 to 3 pounds excess being a safe amount) thus excludingoxygen from the grinding atmosphere. Under these conditions explosionsand fires can not take place. Furthermore, no deterioration due tooxidation is possible in the mill.

In the above-described 36 inch attrition mill with 150 horse power, theprocess of the present invention is capable of producing 800 pounds per9.? a??? sh 2 i e l 1 4 rs ei sl a. temperature of 275 F. In maintainingsuch temperature, from .1 to .5 gallon of water per minute are fed intothe raw material going into the mill or into the mill itself. The amountof Water introduced into the mill in an specific operation to obtain therequired temperature is determined by the amount of water in the rawshell. material fed to the mill, the atmospheric conditions andradiation losses, the clearance settings of the mill, the fineness ofthe finished product, the amount of recirculating load to the mill andthe resistance of the raw material to grinding. The amount of moisturein the raw shell material ordinarily will vary between 8 and 10% and. isgenerally reduced during the grinding operation to 2 to 4% in the hot,dry ground Product obtained. In view of this moisture variation, theautomatic control of the water supply added by means of a thermostat onthe mill provides an extremely simple but positive method of controllingthe temperature While simultaneously efiecting exclusion of oxygen.

The process of the invention not only has the advantage of grinding in anon-explosive and non-oxidizing atmosphere but it also, by automaticcontrol of the temperature in the mill, permits the mill to operate atits maximum capacity without danger of explosion.

An apparatus for carrying out the process of the instant application isdescribed and claimed in the copending application, Serial Number683,226, now Patent No. 2,561,043. A related invention concerned withthe classification of the ground products of the present invention andclaiming such operations either alone or in combination with grindingoperations is set forth in application, Serial Number 683,227, nowPatent No. 2,554,450.

It should be understood that the present invention is not limited to thespecific details of procedures and conditions herein disclosed except asset forth in the appended claims and that it extends to all equivalentswhich will. occur to those skilled in the art upon consideration of thesaid claims.

I claim:

1. A process for grinding to a finely divided condition heat and oxygensensitive organic material in a normally hot-operating, dry-grindingmill which comprises, dry-grinding such material in said mill,introducing water into the grinding mill and vaporizing the same bymeans of heat developed by the grinding operation, creating asuperatmospheric pressure of steam in the mill, dissipating excess heatdeveloped by the grinding operation by means of said evaporation, andpositively excluding oxygen from the mill by means of such steam.

2. The process of grinding vegetable shell material to a size at leastas small as 60 mesh which comprises dry-grinding such material at atemperature above 212 F. in an enclosed mill, introducing water into thegrinding mill and vaporizing the same by means of heat developed by thegrinding operation, creating a superatmospheric pressure of steam in themill, dissipating excess heat developed by the grinding operation bymeans of said evaporation, and positively exeluding oxygen from the millby means of such steam.

3. The process of producing walnut shell flour to a size not greaterthan 60 mesh which comprises, dry-grinding the said shells at atemperature above 212 F. in an enclosed mill, continuously introducingwater into the mill, vaporizing the said water in the grinding mill bymeans of heat developed by the grinding operation, creating asuperatmo-spheric pressure of steam in the mill, dissipating excess heatdeveloped by the grinding operation by means of said evaporation, andpositively excluding oxygen from the mill by means of such steam.

4. The process of producing walnut shell flour of a size not greaterthan 60 mesh which comprises, continuously introducing such shells and asmall amount of water into the mill, continuously dry-grinding suchmaterial in said mill, vaporizing the said water in the grinding mill bymeans of the heat developed by the grinding operation, creating asuperatmospheric pressure of steam in lhe mill, regulating the amount ofwater introduced in direct relation to the temperature in the mill,dissipating excess heat developed by the grinding operation by means ofsaid evaporation, positively excluding oxygen from the mill by means ofsuch steam, and removing the ground nut shell flour from the mill in asubstantially dry form.

5. The process of grinding heat and oxygen sensitive organic materialinto a finely divided form of less than 60 mesh size which comprisesdry-grinding such material in said mill under frictional heat producingconditions which in the absence of cooling would cause overheating thematerial introducing water into the mill and vaporizing the same bymeans of the frictional heat developed by the grinding operation,creating a superatmospheric pressure of steam in said mill, dissipatingexcess heat developed by the grinding operation by means of saidevaporation and positively excluding oxygen from the mill by means ofsaid steam.

6. The process of finely grinding combustible heat and oxygen sensitiveorganic materials which do not appreciably soften at temperatures below300 F. which comprises, dry-grinding such material in an enclosed millunder frictional heat producing conditions which in the absence ofcooling would cause overheating of the material,

continuously introducing a small amount of water into the mill,vaporizing such Water in the mill by means of the said frictionallydeveloped heat, creating a superatmospheric pressure of steam in themill, dissipating excess heat developed by the grinding operation bymeans of said evaporation, and positively excluding oxygen from the millby means of such steam.

7. A process for reducing to a finely divided condition heat and oxygensensitive organic material in a normally hot-operating, dry-grindingmill which comprises, continuously introducing such material and a smallamount of water into the mill, dry-grinding such material in said mill,vaporizing the said water in the grinding mill by means of the heatdeveloped by the grinding operation, creating a superatmosphericpressure, automatically increasing and decreasing the amount of waterintroduced into the mill in response to increases and decreases in thetemperature of the mill, dissipating excess heat developed by thegrinding operation b means of said evaporation, and positively excludingoxygen from the mill by means of such steam.

8. A process for grinding heat and oxygensensitive organic materialswhich do not appreciably soften at temperatures below 300 F. into afinely divided form of less than 60 mesh size which comprisescontinuously introducing such material and a/small amount 01 water intoan enclosed grinding mill, dry-grinding sucn material at a temperatureabove 212 F. in said mill, vaporizing the said water in the grindingmill by means of heat developed by the grinding operation, creating asuperatmospheric pressure of steam in the mill, regulating the amount ofwater added to the material in the mill automatically in response tochanges in the temperature in the mill, dissipating excess heatdeveloped by the grinding operation by means of said evaporation,positively excluding oxygen from the mill by means of such steam, andfinall discharging the substantially dry ground material from the mill.

9. A process for reducing to a finely divided condition heat and oxygensensitive organic combustible materials which do not appreciably softenat temperatures below 300 F. by grinding in a normally hot-operating,enclosed mill which comprises dry-grinding such material in said mill ata temperature in excess of 212 F. at a superatmospheric pressure of atleast one atmosphere, continuously introducing a small amount of waterand vaporizing the same in the mill by means of heat developed by thegrinding operation, creating the superatmospheric pressure by means ofsteam in the mill, dissipating excess heat developed by the grindingoperation by means of said evaporation, positively excluding oxygen fromthe mill by means of such steam, whereby the temperature of the materialbeing ground is prevented from rising to a point at which heatdeterioration of the material being ground will occur and anydeterioration effect from oxygen is avoided.

10. A process for dry-grinding heat and oxygen sensitive organicmaterials which do not appreciably soften at temperatures below 300 F.in a normally hot-operating enclosed mill which comprises, continuouslyintroducing such material into such grinding mill, dry-grinding suchmaterial at a rate creating a temperature above 210 F. but which in theabsence of cooling would overheat the material, continuously introducingwater into the mill in a quantity which through its evaporationmaintains the material at a temperature below that at whichdeterioration thereof occurs, continuously vaporizing such water bymeans of the heat developed by the grinding operation, creating asuperatmospherio pressure of steam in the mill through such evaporation,regulating the amount of water added in the mill automatically inresponse to changes in the temperature in the mill, dissipating excessheat developed by the grinding operation by means of said evaporation,positively excluding oxygen from the mill by means of such steam andremoving from the mill a substantially dry ground materialundeteriorated by the action of oxygen and heat.

JOSEPH W. AYERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,367,895 Schouten Feb. 8, 19211,406,938 Cunningham Feb. 14, 1922 1,708,123 Day Apr. 9, 1929 1,762,241Pontoppidan June 10, 1930 1,795,603 Hussey Mar. 10, 1931 1,976,133Larmour et a1. Oct. 9, 1934 2,008,892 Asplund July 23, 1935 2,050,749 DeMers ----s- Aug. 11, 1936

